feat: V2 source-file analysis upgrades

[corbett3000]

Summary

• add source-file QC, vendor/build heuristics, confidence scoring, and explicit not-on-chip / no-call / ambiguous handling
• add composite analysis and cross-panel rollups for APOE, HFE, MTHFR, CYP2C19, and warfarin PGx
• expand defensible marker coverage with F5, F2, and CYP4F2, and update the report plus docs to surface the new behavior

Verification

• pytest -q
• ruff check src tests